Neoplastic transformation changes the basal concentration of several calcium-binding proteins, calmodulin, S-100, and skin CaBP. The oncodevelopmental calcium-binding protein oncomodulin may also appear in neoplasia, but is different from these others in that it is not found in normal rodent or human adult tissue, and appears in 85% of tumours of diverse origin. It is the long term objective to fit the appearance of oncomodulin into this general perturbation in calcium transport and modulator proteins which must be responsible for some part of the neoplastic phenotype. We must determine whether the expression of the oncomodulin gene is related to the functioning of a particular oncogene, or insertion of a virally borne oncongene into a specific part of the cell genome, or is a general response to neoplastic development. Also of interest is whether transfection of normal cells by DNA from chemically transformed cells activates the oncomodulin gene while inducing neoplastic transformation. This will be achieved by both quantitative and qualitative oncomodulin screening of many different cell types infected by competent, transformation-defective, and temperature sensitive oncogenic viral mutants, or transformed by different chemical carcinogens. The cellular function of oncomodulin will be sought by establishing first the ultra- structural subcellular location of this protein, and by determining whether oncomodulin is responsible for tumour properties, such as invasiveness, by using as a model the normally invasive trophoblast cell, which is one of the few non-neoplastic cells that make this protein.